Inverse emulsion (i.e., water-in-oil) polymerization techniques are well-known. For example, U.S. Pat. No. 3,284,393 discloses a process for thermally polymerizing water-soluble monomers to high molecular weight polymers or copolymers at rapid rates of polymerization using water-in-oil emulsion polymerization procedures in which at least one water-soluble monomer (which may be in aqueous solution) is emulsified in an oil phase by means of a water-in-oil emulsifier and emulsion polymerized under free radical forming conditions to form a polymeric latex in which the oil phase is the dispersion medium. A process such as above-described may be utilized to form acrylamide polymers. However, such a process is not applicable to producing such polymers in particulate form.
Various techniques have been proposed to produce water-soluble polymer particles by utilizing inverse emulsion polymerization. U.S. Pat. No. 3,278,506, for example, describes an inverse emulsion process in which a mixture of an ethylenically unsaturated water-soluble monomer, water-insoluble organic heat transfer medium, free radical polymerization catalyst and a small amount of an antisticking agent are heated to polymerize the monomer. The polymer is sheared by agitation into particles, generally from about 1/16 inch to 2 inches diameter. Such a process, however, is incapable of forming finely divided (e.g., below about 1.0 mm.) particles.
U.S. Pat. No. 2,982,749 describes an inverse emulsion process in which an aqueous solution of a water-soluble monomer (e.g., acrylamide) and a suspending agent (e.g., silica) are added to an oil with agitation to form finely divided globules therein. Polymerization is thereafter initiated under mild agitation conditions. It has been found, however, that particles resulting from a process as described therein tend to agglomerate during formation and have a low viscosity when re-dispersed in water. This renders such products useless in certain applications (e.g., flocculation) where high molecular weight and/or high viscosity aqueous solutions of polyelectrolytes are desirable.